SUMMARY Sepsis and septic shock are a leading cause of mortality, morbidity and health care costs in the U.S. and the world. Both can result from an infection in any organ in the body, including lungs. Sepsis and septic shock can lead to multiple organ dysfunction. Pathogen clearance from multiple organs is dependent on successful innate immune responses in the tissues. Understanding the innate immune mechanisms in the multiple organs is crucial for the development of new therapeutic strategies to attenuate multiple organ damage. In this proposal, we have focused on a primary Gram-negative pathogen, Klebsiella pneumoniae since this extracellular bacterium causes severe pneumonia followed sepsis/septic shock, and the emergence of hypervirulent and multiple drug-resistant K. pneumoniae strains in the U.S. and the world. Our lab has previously reported the NLR family CARD domain containing 4 (NLRC4; IPAF) and NLRP12 as new sensors for K. pneumoniae which can regulates caspase-1 dependent maturation of the inflammatory cytokines, IL18 and IL1?. Since IL-1R1 knockout (KO) mice show greater susceptibility to K. pneumoniae infection than NLRC4 or NLRP12 KO mice these data suggest the role of other NLR proteins. In this context, we found that (1) human organs with pneumonia show greater expression of NLR family pyrin domain containing 6 (NLRP6) inflammasome; (2) (2) mouse organs with K. pneumoniae infection exhibits upregulation of NLRP6 unlike other cell types; (3) neutrophils show the highest expression of NLRP6 in the organs following K. pneumoniae challenge; (4) NLRP6 is most prominent inflammasome for pathogen clearance in the organs in response to Klebsiella pneumoniae infection; and (5) Both T cell subsets and neutrophils produce IL-17A and IL-17F in the organs during K. pneumoniae infection. These observations support a role for NLRP6 in Klebsiella infection-induced sepsis and septic shock. Based on these observations, our hypothesis is that the NLRP6 inflammasome is a master regulator of neutrophil-dependent multiple organ damage following K. pneumoniae infection through the regulation of IL-17A and IL-17F cascade. The Specific Aims are: (1) Establish NLRP6 as a central regulator of multiple organ damage following K. pneumoniae challenge.; and (2) Elucidate NLRP6- dependent IL-17A and IL-17F production in multiple organ injury following K. pneumoniae infection. Identifying that this innate immune cascade is critical to multiple organ damage/failure will lead to a major paradigm shift and ultimately lead to new therapeutic treatment strategies for the treatment of sepsis and septic shock. The proposed research training plan addresses the purpose of the Kirschstein-NRSA predoctoral fellowship (F31) to enable a promising predoctoral student to obtain individualized, mentored research training from an outstanding faculty mentor.